In view of numerous factors such as higher energy prices and environmental concerns, the production of value-added gaseous products from lower-fuel-value carbonaceous feedstocks, such as petroleum coke and coal, is receiving renewed attention. The catalytic gasification of such materials to produce methane and other value-added gases is disclosed, for example, in U.S. Pat. Nos. 3,828,474, 3,998,607, 4,057,512, 4,092,125, 4,094,650, 4,204,843, 4,468,231, 4,500,323, 4,541,841, 4,551,155, 4,558,027, 4,606,105, 4,617,027, 4,609,456, 5,017,282, 5,055,181, 6,187,465, 6,790,430, 6,894,183, 6,955,695, US2003/0167961A1, US2006/0265953A1, US2007/000177A1, US2007/083072A1, US2007/0277437A1, US2009/0048476A1, US2009/0090056A1, US2009/0090055A1, US2009/0165383A1, US2009/0166588A1, US2009/0165379A1, US2009/0170968A1, US2009/0165380A1, US2009/0165381A1, US2009/0165361A1, US2009/0165382A1, US2009/0169449A1, US2009/0169448A1, US2009/0165376A1, US2009/0165384A1, US2009/0217584A1, US2009/0217585A1, US2009/0217590A1, US2009/0217586A1, US2009/0217588A1, US2009/0217589A1, US2009/0217575A1, US2009/0217587A1 and GB1599932.
In general, carbonaceous materials, such as coal or petroleum coke, can be converted to a plurality of gases, including value-added gases such as methane, by the gasification of the material in the presence of an alkali metal catalyst source and steam at elevated temperatures and pressures. Fine unreacted carbonaceous materials are removed from the raw gases produced by the gasifier, the gases are cooled and scrubbed in multiple processes to remove undesirable contaminants and other side-products including carbon monoxide, hydrogen, carbon dioxide, and hydrogen sulfide.
In order to maintain the net heat of reaction as close to neutral as possible (only slightly exothermic or endothermic; i.e., that the reaction is run under thermally neutral conditions) a recycle carbon monoxide and hydrogen gas stream is often fed to the gasification reactors. See, for example, U.S. Pat. Nos. 4,094,650, 6,955,595 and US2007/083072A1. Such gas recycle loops generally require at least additional heating elements and pressurization elements to bring the recycle gas stream to a temperature and pressure suitable for introduction into the gasification reactor. Further, such processes for generating methane can require separation of methane from the recycle gases, for example, by cryogenic distillation. In doing so, the engineering complexity and overall cost of producing methane is greatly increased.
Therefore, a need remains for improved gasification methods where gas recycle loops are minimized and/or eliminated to decrease the complexity and cost of producing methane.